The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Tas govt slams forecast broken cable cost

An energy market analyst estimates a Bass Strait electricity cable outage has cost Tasmania's economy more than half a billion dollars, but the state government discredits the figure, citing positive growth during the period.

Out of operation since December due to a fault about 100km from the state's coastline, the outage has already cost Tasmania some $560 million, EnergyQuest spokesman Graeme Bethune said on Thursday.

The estimates are based on the volume of electricity generated in Tasmania between December and April, multiplied by the difference in power prices between the most recent period and the corresponding period 12 months previously, Dr Bethune said.

But Energy Minister Matthew Groom questioned the credibility of the calculation.

"There is no doubting that costs have been incurred in responding to the issue but not of the magnitude the report cites," the minister said.

The Liberal administration is yet to reveal a cost of the cable outage, but insists it will be made public by the relevant government-run business, Hydro Tasmania.

"All costs incurred in the response will be met by Hydro Tasmania and those costs will not be passed on to regulated power prices," Mr Groom said.